Early weaning (3 to 4 weeks of age) of piglets has become a general practice in pig husbandry systems for increasing the productivity and maintaining the profitability. Early weaning, however, burdens the piglet with a lot of stresses, mainly of environmental, nutritional and immunological origin, combined with a more or less pronounced depression of feed intake and mobilization of body reserves. Maldigestion and malabsorption often aggravate the situation resulting in digestive upsets due to bacterial overgrowth and/or viral infections. These phenomena greatly interfere with the profitability of the enterprise. There is a vast body of literature covering these issues (e.g. VAN DER PEET, 1992; PARTRIDGE, 1993).
The currently used methods to handle those problems aim at the adaptation of the feed to the digestive capacity of the piglet, and/or by improving the acceptability of the feed by the use of specific ingredients (e.g. milk powder and derivates, such as whey and lactose, dried blood serum, flavors), all or not combined with an increase of the energy content of the feed. An increase of the energy content can be obtained among others by including easily digestible or metabolizable fats. The usefullness of medium chain triglycerides (MCTG) in this context is well documented both in neonatal (ODLE, 1999) and in weaned piglets (CERA et al., 1989). The reasons for the usefullness of MCTG is their specific digestive and metabolic fate, reviewed by BACH & BABAYAN. (1982).
Digestive upsets are prevented and/or treated by supplementing the feed with pharmaceutical antimicrobial substances (antibiotics, chemotherapeutics, called antibiotics further on). The combined effects of the above mentioned interventions mostly result in a pronounced improvement of the growth performances (called ‘growth promotion’ further on). This growth promotion is mainly due to, depending on the circumstances, an improved feed intake all or not combined with a better feed conversion (=kg feed/kg gain). However there is a growing concern about the use of antibiotics for growth promotion in animal production systems. Especially there is a well-considered fear for the risk of the emergence of cross-resistance to some last-resort antibiotics used in human medicine (CORPET, 1996; WEGENER et al., 1998). Therefore most of those antibiotics (so called growth promoters) are already or will be banned in the near future in the EU which justify an urgent need for alternatives.
Because there is a general belief that the digestive pathology in early weaned pig is mainly caused by Gram−bacteria (especially E. coli) and that Gram+lactic acid bacteria (Bifidobacteria, Lactobacilli) have a protective and/or antagonistic effect against them, the currently proposed alternatives are selected for their anti-E. coli activity: eg. cupper and zinc compounds, selected organic acids (short chain fatty acids (SCFA, formic, acetic-, propionic acid), lactic, fumaric-, citric, malic, sorbic acid), probiotics (mainly lactic acid bacteria) and/or prebiotics (mainly bifidogenic oligosaccharides, so called NDO's). Cu- and/or Zn-compounds are effective but are not acceptable because their effect on the environment (pollution). Results obtained with pro- and/or prebiotics are unpredictable and generally spoken disappointing (CHESSON, 1994).
Similar problems exist in other animal species and in animals of other age groups.
Only SCFA and the ‘classical’ organic acids are the most promising alternatives for the moment (ROTH et al., 1998). However rather high doses are needed, so that their usefullness is limited by the high cost, their corrosive nature and their averse taste which interferes greatly with the feed intake of the piglets
The antimicrobial effects of fatty acids (FA) in general and their salts (soaps) is already know for decades. A reevaluation of the antimicrobial effects of selected FA (and derivates) is given in the review of KABARA (1978). Special attention was thereby given to lauric acid (C12, a member of the MCFA-family) and derivatives.
Further literature data lead to conclude the relative important contribution of MCFA in the milk-lipid of certain animal species (e.g. rabbit, goat, horse), while in other species the concentrations were low or even nihil as in sow's milk (DIERICK, 1998, literature compilation, personal communication). In most mammals there is a more or less pronounced preduodenal (=not of pancreatic origin) lipolytic activity originating from lingual or gastric secretions. The activity of those lipases is independent of the presence of colipase and bile acids, is active and stable in a broad range of pH's and has a preference for MCFA in milk fat. The preduodenal lipase activity is high in preruminant calves and rabbits, moderate in piglets and absent in poultry (MOREAU et al., 1988). An excess MCFA can have important side-effects: indeed, there are data that they can be hypnotic in new born pigs (ODLE, 1999), and are a strong stimulus for CCK, an intestinal hormone with a pronounced satiating activity what could interfere with the feed intake (LEPINE et al., 1989). A lower feed intake could also be the result of the strong (goat-like) odour and averse taste of free MCFA, although data in this context are scarce and non-conclusive.